Seguenzia formosa is a species of extremely small deep water sea snail, a marine gastropod mollusk in the family Seguenziidae.

Between the ribs the surface is covered with numerous and delicate curved striae, which turn alternately in different directions, so as to give a flexuous character to this part of the sculpture.

The same alternate order is to a great extent observable as to the direction of the striae on the base of the body whorl.

The groove or slit on the upper part of the body whorl, and the opening from the aperture (which characterizes the genus), is wide and deep, terminating in a curved indentation.

[1] This species occurs in the Atlantic Ocean off the Bay of Biscay, off Spain and Portugal at depths between 1,300 m and 1,400 m; also off South-east Brazil.